مطالعه عددي روي جانمايي تك صفحه مستغرق نسبت به لبه‌هاي آبگير جانبي در كانال قوسي U شكل

A numerical study on site location of one vane with respect to the lateral intake edges in a U shape channel bend

هدف از اين پژوهش جانمايي مناسب تك صفحه مستغرق نسبت به لبه هاي پايين دست و بالادست آبگير جانبي واقع در كانال قوسي U شكل و تعيين زاويه مناسب آن به منظور كاهش رسوبات ورودي به آبگير است. در اين راستا با استفاده از مدل عددي فلوينت ميدان جريان حول تك صفحه مستغرق واقع در لبه پايين دست آبگير شبيه سازي و با نتايج پژوهش آزمايشگاهي منتصري (2008) صحت-سنجي شده است. مدل آشفتگي مورد استفاده است. پس از صحت سنجي مدل، اثر موقعيت هاي صفحه مستغرق نسبت به لبه هاي پايين دست و بالادست آبگير و اثر زواياي مختلف صفحه بر الگوي جريان و الگوي تنش برشي بستر بررسي شده است و موقعيت و زاويه مناسب صفحه بر اساس ميزان تاثير صفحه روي وسعت ناحيه پر تنش اطراف صفحه، نواحي كم سرعت اطراف صفحه در تراز كف، كاهش ابعاد ناحيه زيني واقع در لبه پايين دست صفحه و چگونگي انحراف خطوط جريان انتخاب شده است. نتايج نشان مي هد بهترين حالت قرار گيري صفحه در لبه پايين دست حالتي است كه ابتداي صفحه دقيقاً در مقابل لبه پايين دست آبگير با زاويه اي در حدود 20-25 درجه قرار دارد و بهترين حالت قرار گيري صفحه در لبه بالادست حالتي است كه انتهاي صفحه دقيقاً در مقابل لبه بالادست آبگير با زاويه اي حدود 17 تا 20 درجه قرار دارد.

The purpose of this paper is determination of appropriate location of the one submerged vane with respect to the downstream and upstream edge of the lateral intake in a U shape channel bend and choice the best angle of vane for reduce the sediment entry to the lateral intake. In this order we use the Fluent software to numerical simulation of 3D flow pattern around the one vane that locating in front of downstream edge of a lateral intake in a U shape channel bend. The results of numerical were verified with the existing experimental data. Comparison of the predicted x velocity and y velocity field with laboratory measurements indicates that the model capture experimental trend with reasonable accuracy. Computations are performed using Reynolds Stress Model. After model verification, the effect of different position of the vane with respect to downstream of intake (the first, middle and end point of vane is in front of downstream edge of intake) and upstream edge of intake (the first, middle and end point of vane is in front of upstream edge) and effect of different angle of vane (15, 17, 20, 25, 30 degree) on flow pattern and shear stress pattern of bed is considered. The appropriate position and angle of the vane has been selected by effect of the vane on area of high shear stress zone and area of low velocity contour around the vane and reduction of dimension of saddle point near the downstream edge of lateral intake and situation of stream line around the vane and in front of the intake at the bottom of the channel. The results show the best position of vane with respect to downstream edge of lateral intake is the case that the first point of vane is in front of downstream edge of intake and the best position of vane with respect to upstream edge of intake is the case that the end point of vane is in front of upstream edge of intake. Also the results show that the appropriate value for angle of attack of the vane at downstream edge of intake (the first point of vane is in front of downstream edge of intake) is about 20-25 degree and optimum value for angle of attack of the vane at upstream edge of intake (the end point of vane is in front of upstream edge of intake) is about 17-20 degree.